I updated mine from S670330N to S21804i without issues.
From what I've read, once you're on S670330N, you're at a firmware version that, if you couldn't update past that, is good enough for the DOM to not have any premature wearout or any other failures that could be avoided with firmware updates.
From what I've read, once you're on S670330N, you're at a firmware version that, if you couldn't update past that, is good enough for the DOM to not have any premature wearout or any other failures that could be avoided with firmware updates.